There once was a hooker named Sally but her colleagues new her as Sally Scab Fanny as she always had a grotesquely scabby fanny.
One evening she was turning tricks under her usual street light and she picked up a bit of work with a typical nerdy sort of loner dude.
They went off up to her room and she laid down on the bed. She informed the guy that he better go shower before they could get into it.
The reason Sally would instruct the guys to go shower was so that she could get her knickers off and pick all the scabs off her fanny to aid in lubing herself up. Once she had picked all the scabs off her fanny she would put them in a small plastic bag and hide them under the bed.
Her customer returned from the shower and asked how much the root would be, Sally informed him it would be fiddy dollars. He ripped off his clothes, hopped on the bed and slid on in (after fitting a rubber of course). They went at it for a bit and then lay on the bed exhausted, they both fell asleep pretty quickly.
Sally Scab Fanny woke to find the man had gone, but being the gentleman he was he had left her the money and a note. Sally noticed that the man had left $52.50 and she thought that was strange, she never normally got tips. She picked up the note and read it:
"Thanks for the amazing root Sally it was a bargain at $50 and it really wore me out. While you were asleep I got hungry and found a plastic bag under the bed with chips in it. Sorry I ate them all but I left you $2.50 extra to cover the cost of them."
I first heard that joke in Primary School It's old and pretty shit, but still it is a classic.